1. Field of the Invention
This invention relates generally to the art of manufacturing film processing rollers of the type useful in processing self-processable type film units, and, more particularly, to methods for providing such rollers with a smooth film-contacting surface in the form of a thin, relatively high-friction, traction coating.
2. Background of the Prior Art
Fully automatic photographic systems for use with self-processable type films are well known in the photographic field and have been extensively described in the patent literature. These systems, such as Polaroid Corporation's "SX-70" and "Pronto!" cameras, are designed to automatically produce finished, waste-free photographs following their actuation. They accomplish this task through the use of specially designed interdependent function providing sub-systems which are organized to carry out a programmed series of sequential operations that ultimately result in a finished photographic print. The order of operations, following system activation, usually begins with exposure of a film unit at some suitable predetermined location within the camera. The exposed film unit then is advanced from the exposure location into engagement with a film processing sub-system or apparatus. The film processing apparatus functions to transport the exposed film unit to the exterior of the camera where it is accessible to the user and to spread a processing fluid across a selected photosensitive layer of the exposed film unit while the film unit is being transported to the exterior of the camera.
Film processing apparatus that have the capability of performing the foregoing functions are well known in the prior art and are extensively described in, for example, U.S. Pat. No. 3,776,118 issued to John J. Driscoll et al. on Dec. 4, 1973 and entitled "Photographic Film Processing Apparatus" and in U.S. Pat. No. 3,766,842 issued to James M. Whall on Oct. 23, 1973 and entitled "Photographic Film Processing Apparatus". Such film advancing-fluid spreading apparatus typically include a roller assembly comprising first and second rotatably mounted juxtaposed elongated rollers which are resiliently urged toward one another. A pair of annular collars are generally provided on the first roller to define a minimum gap between the rollers to facilitate the initial introduction of a leading edge of a film unit between the rollers. The first roller is adapted to be selectively driven by a motor of the camera and, when so driven, its anular collars impart a rotary motion to the second roller. At least those portions of the two rollers adapted to contact one another are formed of a relatively low friction, impact resistant material, such as stainless steel, while at least the sheet-contacting facing surface of the first roller is formed of a relatively high friction material such as urethane. The urethane coating operates to provide a relatively high traction force between the first roller and the film unit to transport the film unit outside of the camera and the stainless steel provides the strength necessary to withstand the pressures generated during the transport and fluid spreading phases. The stainless steel in addition to its strength also possesses desirable corrosion resistent characteristics.
Because of the nature of the functions of such film processing apparatus, the pressure-applying rollers which are used in them must be manufactured to extremely tight tolerances. For example, their outside diameters are typically held to a tolerance of within a few tenths of a mil. Obviously, this tolerance requirement adds to their overall expense. The urethane coated drive roller in particular represents a major portion of the total cost of such film processing apparatus not only because of the tolerance requirements but also because of the necessity of having the relatively high-friction urethane coating.
The present method of manufacturing such urethane coated drive rollers involves a batch processing electrostatic vapor spray technique. With the electrostatic spray technique, a group of finish-machined stainless steel top rollers are individually indexed to a spraying station where a layer of urethane is deposited on their exterior surfaces by spraying electrically charged vaporized urethane onto each roller's surface as the roller is rotated and electrically charged at a polarity opposite to that of the vaporized urethane. With this process, only one roller at a time can be coated with urethane at any one spray station. After the urethane coating has hardened, the roller is then finish ground to reduce the thickness of the urethane coating to a predetermined value. With this process, the cost of applying the urethane coating using the electrostatic spray technique is between 30% and 45% of the total cost of the roller.
While the electrostatic spray process produces functionally acceptable film processing rollers, it is obviously desirable to reduce the cost of manufacturing such rollers by using other methods.
One well-known method of applying plastic coatings, such as polyethylene and elastomeric vinyls, to wire is by cross-head extrusion. However, the materials involved in wire insulations are generally softer than those required for the traction coating of film processing drive rollers of the type previously described. Moreover, the tolerances on the thickness of wire insulation coatings are not as critical as those for film processing rollers.
It is also known that the cross-head extrusion process has been used to apply elastomeric coatings to handrails which are used in the transportation industry. These coatings, however, are generally relatively thick-on the order of one-eighth of one inch.
It is a primary object of the present invention to provide a high volume, low cost methods for manufacturing a photographic film processing roller.
It is another object of the present invention to provide methods for providing a relatively thin traction coating on a roller suitable for use in a photographic fluid processing and film transport apparatus.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the methods possessing the sequence of steps, apparatus, and materials which are exemplified in the following detailed description.